Endogenous IGF-I and α v β 3 integrin ligands regulate increased smooth muscle growth in TNBS-induced colitis

• Published in: American journal of physiology: Gastrointestinal and liver physiology 2009-06, Vol.296 (6), p.G1230-G1237
• Main Authors: Hazelgrove, Krystina B., Flynn, Robert S., Qiao, Li-Ya, Grider, John R., Kuemmerle, John F.
• Format: Article
• Language: English
• ISSN: 0193-1857; 1522-1547
• DOI: 10.1152/ajpgi.90508.2008

Endogenous insulin-like growth factor-I (IGF-I) regulates intestinal smooth muscle growth by concomitantly stimulating proliferation and inhibiting apoptosis. IGF-I-stimulated growth is augmented by the α v β 3 integrin ligands vitronectin and fibronectin. IGF-I expression in smooth muscle is increased in both TNBS-induced colitis and Crohn's disease. We hypothesized that intestinal inflammation increased vitronectin and fibronectin expression by smooth muscle and, along with IGF-I upregulation, increased intestinal muscle growth. Intestinal smooth muscle cells were examined 7 days following the induction of TNBS-induced colitis. Although α v β 3 integrin expression was not altered by TNBS-induced colitis, vitronectin and fibronectin levels were increased by 80 ± 10% and 90 ± 15%, above control levels, respectively. Basal IGF-I receptor phosphorylation in inflamed muscle from TNBS-treated rats was increased by 86 ± 8% over vehicle-treated controls. Basal ERK1/2, p70S6 kinase, and GSK-3β phosphorylation in muscle cells of TNBS-treated rats were also increased by 140–180%. TNBS treatment increased basal muscle cell proliferation by 130 ± 15% and decreased apoptosis by 20 ± 2% compared with that in vehicle-treated controls. The changes in proliferation and apoptosis were reversed by an IGF-I receptor tyrosine kinase inhibitor or an α v β 3 integrin antagonist. The results suggest that smooth muscle hyperplasia in TNBS-induced colitis partly results from the upregulation of endogenous IGF-I and ligands of α v β 3 integrin that mediate increased smooth muscle cell proliferation and decreased apoptosis. This paper has identified one mechanism regulating smooth muscle hyperplasia, a feature of stricture formation that occurs in the chronically inflamed intestine of TNBS-induced colitis and potentially Crohn's disease.